4-amino-3,5-dichloropyridine-N-oxide is prepared by the following steps:A sealed Carius tube containing 4-nitro-3,5-dichloropyridine-N-oxide (36) (0.4 g, 1.9 mmol), aqueous ammonia (1 cm3 of 0.88 gi-l solution) and acetonitrile (1 cm3) was heated in a rotating oil bath at 70 OC for 3 h. The mixture was filtered giving a solid (0.1 g) and a filtrate, which was extracted into DCM, dried (MgS04) and evaporated giving a residue (0.0 g). The solid obtained from the filtration was recrystallised from hot methanol giving 4-amino-3,5-dichloropyridine-N-oxide (0.1 g, 30%), m.p. 210 oC from MeOH) (M+ found 177.9701. C5H4Cl2N20 requires M+ 177.9701); IR spectra no. 30; mass spectra no. 37; nmr spectrum no. 45.
4-Amino-3,5-dichloropyridine N-Oxide is the impurity of the drug Roflumilast (R639700), which is a selective phosphodiesterase 4(PDE4) inhibitor, antiasthmatic.
